Diagnostic techniques for determining the operability and efficacy of three-way catalytic (TWC) converters are commonly used on vehicles to comply with federal and/or state emission control regulations. Typically, such techniques attempt to measure catalyst oxygen storage capacity by utilizing a Heated Exhaust Gas Oxygen (HEGO) sensor positioned upstream of the TWC converter and a HEGO sensor positioned downstream of the TWC converter to detect the oxygen equilibrium concentration in the exhaust gas entering and exiting the converter. An electronic engine controller receives the signal generated by each of the sensors and determines the operability and/or efficacy of the converter as a function of the output of the two HEGO sensors.
The inventors herein have discovered that such techniques suffer from a number of deficiencies, the most notable of which is the lack of a complete correlation between oxygen storage capacity, which is determined by way of dual HEGO sensors, and catalyst conversion efficiency. In addition, the use of the aforementioned technique depends upon the volume of the converter and may not work satisfactorily for small-volume, close-coupled catalysts like those planned for use on certain low-emission vehicles. In addition, certain types of fuel additives and naturally occurring chemicals, such as fuel sulfur, can adversely affect the performance of the aforementioned techniques.
It is accordingly an object of the present invention to provide a system for diagnosing the operation of a catalytic converter which overcomes the aforementioned deficiencies of known diagnostic techniques.